The Research On The ECAP Experiment For Consolidation Of Al Powder And The Improvement Of Device

Powder metallurgy process can make the powder materials consolidation for a certain shape,size and performance of products.However,because of the production process by powder metallurgy technology is more complicated.And there will exist more pores inside product.Relative to other dense materials,the plastic deformation ability of products is weak.In the subsequent processing deformation process,there will accumulated damage.It is difficult to produce larger effective strain,thus affects the grain refinement effect and reduce strength and toughness.So it affects the mechanical properties of the material,which influences the property of material.This paper combines the characteristic of powder plastic with equal channel angular pressing(ECAP),put forward a new way called powder in tubes.This paper uses the pure aluminum powder as the experimental material.At low temperature,The experiment successfully achieves the powder particles consolidation as a high density of bulk materials.The evolution of microstructure after each pass of different route is observed by using optical microscope technology and transmission electron microscopy technology.Studythe internal microscopic structure of sample changed before and after deformation characteristic.Then the mechanism of densification and grain refinement are analyzed.The results indicate that the densification and powder grain refinement of samples are improved after four passes by different routes of extrusion.From the experimental results,the densification and powder grain refinement effect of first past is most obvious.After the first pass,the samples relative density reach to 0.960 and have no obvious pores.The grain size become from the original about 40 ?m down to 22.64 ?m.Followed by a few passes,the densification and grain refinement of samples are further improved.But the extent of increase is relatively slow.From the results,the effect of densification and powder grain refinement by A and Bc route are better than the C route,that is mainly related to three extrusion method of shear mode.From the results of microhardness with different passes and surfaces by different routes,the first pass of sample cross section X average microhardness reach to 41.25 kg/mm2.Followed by a few passes,the microhardness is also increased.The evolution of microstructure at plane X and Y after each pass of different routes are observed and the microstructure for Bc route with different passes are observed by TEM observation.Then the refine and strengthen mechanism are analyzed.Analysis is that the hydrostatic pressure,shear characteristics and strain accumulation are the main factors of grain refinement and densification in the ECAP process.From the microstructure of the sample at cross section of the fourth pass by C route,the ingredient at borders and central region is different;from the result of the second pass by A route,the crack appears in the internal of the sample.There are many problems in ECAP.Extrusion sample forming a smaller outer round at the corner through the mold when it is forced back pressure.It can make extrusion sample gain greater plastic deformation,so the capacity of plastic deformation can be significantly improved.which can prevent crack and make brittle material plastic deformation.To brittle material,exert back pressure can minimize extrusion temperature,which is easier to get fine grains.Using slip-line theory,the analysis formula of extrusion force in ECAP with back pressure during a single pass was derived,which provides a reference for strength design of equal channel angular pressing with back pressure.Based on the extrusion force,protruding die,female die and die pad were designed and manufactured,which makes a foudation for the next BP-ECAP experiment.